To western



s. 5. wnLuAMs, JR. TELEPHONE EXQHANGE SYSTEM.

women-Juan DEC. 31.1919.

Patented June 7, 1921.

2 SHEETS-SHEET 1.

s. B; WILLIAMS, JR.- TELEPHONE vEXCHANGE SYSTEM.

APPLICATION ruin-150.31, 1,919.

Patented June 7, 1921.

2 SHEETS-SHEET 2 SAMUEL B. WILLIAMS, Ja onBnoonLY-innriw YORK, AssIenoR "ro weswma" in V ELECTRIC COMPANY, rivconronn'rnn, or NE YORK, 1v. 2., A CORPORATION.

NE YO To all whom'z't may concern/.1 7 .c .7 I

Be it knownthat I, SAMUEL B. .WrLLraMs,

Jr., a citizeniof the United States, residing at Brooklyn, in the county of Kings and" State of New York, have invented certain new and useful Improvements in Telephone Exchange Systems, ofwhich thefollowingis a full, clear, conc se, and exact description.

This invention relates aim-0mm tele-i phoneexchange systems, and morefparticua larly to systems in which line finders are employed for establishing aconnection be tween a calling line and anidle trunk,

a In automatic telephone exchange systems which employ power-driven line finders op crating in conjunotionwith contact banks of the well-known panel type, the connection between a calling line and .an'idle trunk may be, in some cases, slower than is desirable, since in the switch of standard construction, the contact bank contains 500 ter- 7 minal sets served by ten multipled brushes i on a common operating shaft. After a given" brush has been; selected, if the calling'line' is represented in the bank by'the last terminal-set, it is necessary for the selected brush set to advance over fifty terminals iniorder toaccomplish the desired connection. 1

It is an object of the present invention to materially reduce the average time'requiredin establishing a l ne to trunk connectlon by a novel arrangement of the grouping in the contact banks, without changing the nee chanical construction of the apparatus A feature of the invention is a special sub-- grouping arrangement within the .manr

- group of lines served bya line finder. The.

to contact banks in which the 'line of the resultant subgroups are then slipped to. the various finder contact "banks in such -a manner that normally ai -shortenhuntingperiod will be required. I c

A further feature of the invention resides in the provision of allottersindividual to the various subgroups. These allotters are arranged to, start finders which, have access originating subscriber appears as an early choice. If all the first choice finders of given subgroup are busy, a finder which is normally a first choice for theallotter of some other subgroup may be started in-oporation.

' An additionalteature of the invention re sults from an arrangement whereby the alavailable'for use. I

TELEPHgLTEEXCHANGE SYSTEM; v

c Specification o f l i e tters Patent. Patented J 1921; Application fil ed 'Decembr '31, 1919'. Serial in. 348,510., v i

and allotja first choice switch in, case that a first choice switch has ;meanw hile become j The obj sets and features I or the invention have been described in connection with a five hundred point power-driven panel bank line finder, in order to clearly show theadvam stages resultantzfrom a specific employment.

of this invention. S ince the invention is obviouslycapable of avarietyof uses and shows, diagrammatically, the general-out line of the system,

7 "Referring now to Fig. 3, there 'areshown two groups of panel-bankpower-driven line finders provided withpcommon trip magnets 1 andf2n The mechanical construction of: these switches is similar to that shownand described in Patent No.,1,177,044, issued on Warclr28, 1916, to J. L. MCQIRLITlQJQ Each v I c c It is thought that the invention will best switch includes/a vertically movablebr'ush shaft 3 carrying ten?brush"sets,:'three of which are indicatedat 4L, 5 and 6; 'VVhen' magnet 1, for instance, is operated, subsequent upwardfmovementby a brush shaft- .willtrip thecsecond set 'ofbrushesinto' op'-" erative engagement 'with'the contact bank served by it, which contact bank comprises av main group of fiftylineterminals. Inaccordance with thepresent invention, each main group of terminals is divided into two subgroups oftwenty-five lines each;

Qjne group of line finders is shown as hav in g access to the terminals on the panel bank indicated generally at A, while 1 another group or finders is shownas having access. to the panel bank indicated generally at B.

ojbe' o ser ed that the e is individual tothe Referrinfginow to the first main group, it is I first subgroup of such main group which is indicated at 7, an allotter, generally indicated at 8 which, upon moving in a clockwise direction, serves to allot, as first choices, the finders having access to bank A. The subgroup 7 contains numbers from O to 24:. Therefore, if a call is originated in subgroup 7, allotter 8 will operate to put into operation one of the finders bank A as a first choice, and, therefore, this finder will have to travel over a number of lines not exceeding twenty-five, in order to establish the desiredconnection. Should a line in subgroup 9 of the first-named group of one hundred lines initiate a call, an allotter 10 would put into operation one of the finders which has access to terminal bank B, provided that there is one of these finders idle and available for use. It is to be observed that the lines insubgroup 9, which are numbered from 25 to $9, appear in the lower half of the first group of terminals in bank B. Therefore, if a finder serving bank B is put into operation, a maximum of twenty-five steps will be all that is required to establish the desired connection.

If, at the time a subscriber at subgroup 7 initiates a call, all the finders which serve bank A. are busy, the allotter 8 will be advanced into a position to allot a finder, in group B. In this case, the finder will have to advance over the terminal sets of lines 25 to 4C9, and will then have to search for the proper line. In this case, it would be possible that the entire fifty steps would have to be taken. It is obvious that by an arrangement of this kind, it would usually be possible to establish a connection without requiring more than twentyfive steps as a maximum.

Inspection of the second main group, which comprises subgroups 11 and 12, will show that the arrangement is substantially similar to that in the first-named group, that is, the fifty-line group is divided into two subgroups of twenty-five lines each, and that the terminals of these lines are slipped between banks A and B in twenty-five point subgroups.

From the foregoing, it is believed that the detailed description which will now be given may be readily understood. Referring now to Fig. 1, 13 and 14 indicate substations in different subgroups of the same main group of fifty lines. The controlling relays for this particular main group of fifty lines are indicated at 15, 16, 17 and 18 respectively. Relays 19, 20, 21 and 22 are individual toanother main group of fifty lines. As shown, substations 13 and 14 are in the second fifty group of lines. There is provided for each succeeding main group, a set of relays common to the group and correspondingto relays 15, 16, 17 and 18. The e g p relays are interconnected in a serving manner which should be readily understood from the disclosure of the interconnection of the various relays in the two groups which are shown. In Fig. 2, brushes 23, 24, 25 and 26 are the brushes of an allotter controlled by a stepping magnet 27, this allotter being under the control of the second subgroup of eachof the ten main groups. The allotter, comprising a stepping magnet and brushes 29, 30, 31 and 32and their corresponding terminal banks, is arranged to be controlled by lines in the first s bgroups of the ten main groups. The mechanical construction of the allotters is substantially similar to that of a switch shown in an application, Serial No. 317,126, filed August 13, 1919, by Messrs. O. F. Forsberg and R. M. De Vignier.

Let itbe assumed that the subscriber at substation. 1.3 desires to init ate a call. He will remove his receiver from the switchhook, whereupon a circuit will be completed for line relay 33, through the armatures and back contacts of cutoff relay 3-1. The energization of relay 33 completes a circuit from grounded battery, winding of relay 15, armature and back contact of relay 16,,

provided this relay is in its normal condition, conductor 35, winding of relay 36, armature and front contact of relay 33 to ground. Relays 15 and 36 are cnergizedin this circuit.

It is also to be assumed that the switch shown to the right of Fig. 1 is a switch which serves terminals in bank B and that this switchis idle. It will also be assumed that the allotter controlled by magnet 27 has its brushes 23, 2e, 25 and 26 in engagement with their first terminals respectively. Under these assumptions, the energization of relay 15- completes a circuit from grounded battery, left-hand winding of slow-to-release relay 17, left-hand armature and front contact of relay 15, left-hand armature andback contact of relay 19, assuming this relay to be deenergized, conductor 37, inner righthand armature and back contact of relay 38, left-hand armature and back contact of relay 39, left-hand armature and back contact of relay 10 to ground. Relay 17 is energized in this circuit and locks up through its right- -hand winding and right-hand armature and that no other group relays. corresponding to relays 17 and 21 can be energized to start finders until the operation has progressed to a proper stage. The energlzatioll. of relay 17 also completes a circuit for trip magnet 18 extending from grounded battery,

windingof magnet 18, right-hand armature and front contact of rela 17 to ground over the path described; agnet 18 operates a common'trip rod-s0 that as 'soon'aas any finder reg'ardle'ss of-whether it serves bank A'or bank Bis started, the second set of brushes on suchfinder will be tripped. The energization of-iielayifi also completes a l circuit from grounded" battery, winding of relay 42, outer 'ri gh t-hand'- armaturefand front contact of"relay-". '38,- conductor" t3,, inner left-hand armature and front contact of relay 17, armature and front fcontact of relay 36 to ground. -Relay 42is energizedin this circuit and completes a circuit "from grounded battery, winding of relay j lei, co tact of sequence switch spring45, conductor 4L6, allotter brush 26 a'ndits associated contact, right-hand armature and :frontcontact of relay 42 to ground. Relay 44' i's ener gized in this circuit andconrpletesacircuit from grounded battery, power magnet-of sequence switch 47, lower contact of se quence switch spring 48, right-hand armature "and front contact of relay l l to ground, for 'moving thissequence switch out of position 1 and into position 2.

In position 2 of sequence switch 4 7, a; circuit is completed from grounded battery,"

' winding ofup-drive magnet 49," sequence switch contact. 50, righthand armature and front contact of relay ii-to ground. Under the control of 'magnet 49, the brush shaft is moved upward and the second set of brushes is tripped, after 'which, the line hunting" movement takes place;

After sequence switch eTleaves position i 1. th original "energizing circuit for 1 test relay iis broken at sequenceswitch spring 45, but this relay remains locked up aslong v as test brush 51is -engaging test terminals 7 52 associated with busy or non-calling lines,

since ground will be found on these test terminals, to which it is supplied through the armatures and backcontacts of the line relays associated with such lines. iiDue to the fact that the line relay of-the callingline is energized, no ground will be found on the test terminal 52' associated with the calling line, and therefore, when test brush 51" engagesthe test terminal offsuch line, this branch of the locking circuit of the relay 44: is opened. Relay i4 is maintainedfenergized, however, a moment longer, due to the closure of a circuitthrough the upper contact of sequence switch spring 58 by way of conductor 54, commutator 55 and brush56 to ground. When, an instant later, brush 56 7 engages an insulating segment ofcommuta tor 55, at which time the brush set willbe accurately centered on the calling line terminals, the circuit of relayefl is broken, and I this relay deenerglzes, openlng at its right hand armature, thecircuit of up-drive mag- 7 net 49 andallowing thebrush set to come to rest At itsriglit-hand armature and back contact, relay 4 1 completes a circuitfrom *grounded battery, power magnet of sequence switch 17, upper contact of sequence switch springi48, armature and back contact of "re layALtO grOun'd for. moving this sequence other switcheout of position 2 a'nd into some circuit controlling position. t -.The sequenceswitch 47, in practice, would be utilized a) control the vari ousselective operations of a district selector lorsome corresponding switch. Sincefthe invention is not concerned with the operation ofsubse quentlswitches, it has not been considered necessary to. show 1n what POSltlOIlSSGQllGIlCG switch 47 comics to rest, nor what/operations 7 take place in the various intermediate positions of such'seque'nce switch; Y It is to be observed thatras soon as th line finder moves out of its normal position,

commutatorbrushf56 engage's'a' commuta-- commutator: segment i 57 commutator brush :56 to 'ground.- Relay 39. is'energized in this circuit and locks up through its inner righthandarmaturelandfront contact :to-ground through-allotterbrush 24 and its associated *contact, conductor 61,upper left-handcom' tact 'ofsequence'switchspring 62 to ground.

Relay 39' will, therefore, remain energized until test brush 24of-the allotter is brought into engagement with a terminalindividual to a finder switch which is standing in poisition 1 andtherefore idle.

The energization 'ofrelay 39 completes'a circuit'fr'om grounded battery, winding of stepping magnet 27 armatureand back contact ofmagnet 27 outer right-hand armature and frontcontactqof relay.39 .to ground. 'Magnet27 islenergized in this circuit and continues to. interrupttits own circuit until -anidle finder has been found. 'As shown in Fig; 2, theallotter switch controlled bymagnet 2.7 has access tothree B finders as first choice, after which fit'has access to three A finders. The number of finders is, of course, immaterial, and if the contact Ibanksserved by theallotter brushes comprise twenty terminals, the first ten would then lead to first would lead choice finders and the second ten tosecondchoice finders; 1 1 V fi-Aaer the allotter brushes pass overithe first three terminals, theywill thenstart to test for an idle finder in the-A group and may come to restin a position to allotfsaid Afinder. Assuming that the A finder Whose circuits are partially shown inFig; 1, is the,

'only in the A group whicli is idle,;magv i 'relay.17, conductor 66, left-hand net27 will continue to advance the allotter brushes until brush 24 engages its sixth terminal. No ground will then be found on such. sixthlterminal, since lead 6 1 is open at sequence switch contact individualto v such finder.

group, conductor 63which is multipled to the lower right-hand contact of allthe sequence switchv spring contacts 62 associated with B finders, and thence to ground at the.

contact of the particular sequence switch spring 62 whose associated sequence switch is in position '1. In this case, the allotter will advance until such idle finder has been seized, whenit will come to rest and await the initiation of another call in the second subgroup.

As soon as relay 39 was energized, due to the fact that an allotted finder had started out of its normal position, a circuit was completed for relay 16, extending from groundedbattery, winding ofrelay16, outer left-hand armature and front contact of armature and front contact of relay 39, left-hand armature and back contact of relay 10 to ground. Relay 16 is energized in this circuit and locks up through its right-hand armature and front contact to conductor. 67 and will remain energized until the line is found, since lead 67 is multipled to the upperright-hand contacts of all sequence switch springs 65 in the A group and all sequence switch springs 62 in the B group. Relay 16, therefore, prevents relay 15 from being again energized until the particular line-calling. in the main group to which relay 16is individual, has been found.

The energization of relay 39 also opened the circuit for relay 38, and this relay de energizes and prevents the reenergization of relay 42 to prevent the starting of another finder. The locking circuit for relay 12 was broken when relay 39 was first energized.

Vith the allotters in the position shown in Fig. 2, if the subscriber at substation 14.

desires to initiate a call, the operation of the system is fundamentally similar.' In this,

case, relay 68 would have been energized in series with relay 15' upon the energization of line relay 69. The subsequent energization of relay 17 would then have completed a circuit from: grounded battery, winding of relay 7 O, middlerightehand armature and front contact of, relay 38, which; would have been energized as previously described, con: ductor 71, middle left-hand armature and front contact ofrelay 17, armature and contact of relay 68 to ground. Relay. 70would have been energized and throughits righthand armature would have supplied ground through allotter brush 32 and its associated contact, over conductor 72, to sequence switch spring 73 and the winding of line relay 74 to groundedbattery, to cause the starting of a finder serving the A group, in which the terminals of the calling subscribers line appear in the lower half of the main group of fifty lines. 7 7

It is to be observed that, while either of the allotter switches is in operation, that is, while either relay 3901 relay 410 isv ener gized, no finder switch can be started since the circuit for relay 38, which serves to connect throughthe controlling leads for the start relays 42 and 70 respectively, is open when the left-hand armature of either relay 39 or relay 40 is inits attracted posi tion. Therefore, no finders will be started. until both allotters haveseized terminals associated with idle finders.

If a second call is orginated in the same main group before a line which previously originated a call has been seized, the continued energization of relay 16 will prevent the circuit of relay 15 from being completed. The circuit of relay 1?, therefore, cannot be completed and the trip magnet of the group cannot be operated. If a call is originated in some other group while a finder is hunting, it is to be observed that the resultant energization of relay lfi, which causes the deenergization of relays 15 and 17, allows the series controlling. circuits, which are extensions of conductors 3'? and 41. respectively, tobe completed to their main groups. P herefore, other'main groups may originate calls while a finder is hunting, provided that both the allotters 39 and 10 have come to rest in position to allot idle finders.

from the fore 'oirw it is obvious that in one main group only one call can be originatedat a time and thatany other calls which are originated must wait until a preceding line has been seized. Incase a number of calls in the same main group are originated simultaneously or in rapid succession, only one finder will be started and it will seize the line which is lowest in the group. After this finderhas come to rest and provided that no other group has taken precedence, the fact that there are still lines in calling'condition, as shown by the energization of line relays, will cause another finder to be started as soon asit has been allotted.

In case of simultaneous calls in different main groups, the call in the main group containing lines ofalower' numerical order will take precedence, since relays 19 and21' common to such main'group Wlll havefirst group, the energization-oflrelay 2Ov will completely disclose the circuits associated cause thedeenergization of relays 19 and 21, and these relays upon deenergization will connectthrough the group controlling leads 37 and 41' so that a new finder may at once be started in search ofthe calling line in the groupqwhich is, next in precedence,

providing'that the allotters have taken their 7 into position 18; i V V ,In position 18-ofsequence switch 47 a cirpositions as previously described. There I shouldbe very little delay in the allotment of finders since the allotter is started into operation just assoon as theallotted finders brush shaft leaves its normal position,-as

was previously brought out in this descrip tion. 7 I

- The only case in which two finders may be started simultaneously occurs when two lines in difi'erent subgroupsof the same mam groupinitiate" calls 'snnultaneously or in rapid succession: Let} it beiassumed, for example, thatllines 13 and 14 originate calls in rapid succession. If line 13 was the first to originate the call, the operation of thesystem would be'the same as just described and a B finder would be started. It now, substation 14:: originates 'acall'before the B finder has moved out of it'snorrnal position,

that is before relay 39 can become ener gized, a simultaneous circuit will become f 'pleted for relay: 70'. which will operate. to start an finder. .However, since both finders serve thesamema-in group, in each case the second set of brushesw'ill be tripped and botlrfinders willcontinue in operation until each has seized one of the lines.

I It would, of course, be possible to have only one finder out of the entire combined A and B groups idle. In this case the two j allotters would both-be standing in a posi-, tion a to allot the same. finder. In this case, "obviouslyfonly jone finder would be I started and only one line would be seized, but no harm would'be'done since when the line had been seized and the sequence switch associated with such finder-had m'ovedout of;

position 2, relay 16 would'bedeenergized and, if meanwhile another finder had be call and put into operation the B finder. shown in'Fig l, it is to be'observedthat when the line associated: with substation 13 was found, cutoff relay '34: was .-e'nergized by means of suitable circuits and causedjthe' deenergizationof'relay As soon as se-v quence switch 4 7- moved out of position 2, relay lfi'was deenergized. 1 Relays 15 and o36,"however, do not again become energized, 1 since ground 1s now absent at the armature and Contact of relay 33., This leaves the 'subsc'ribers relaysi'and the subgroup and group relaysin 1111611 normal conditlon and ready for reoperation.

T lt has not been considered necessary to i with the line finder. It issuificient to state that-when the connection is no longer de.-'

'sirechthe restoration of the district or simis cuitisfcompleted from grounded battery, winding of down-drive magnet 75, contact 47 to be advanced of sequence? switch [spring ,76. to ground.

The brush shaft is restored to its normal I position under the control ofmagnet 75, and when fully restored a circuit is completed from grounded battery, power magnet of sequence switch 927, upper right-hand contact of sequence switch spring 48, conductor "'77, normal'commutator segmen't 78, com;

mutatorbrush 56 to ground, for-moving the sequenceswitch outofposition 18 and into :pOSitiOIl it may be r position 1, from which realloitted forusef "What is claimed ,is J

1. Ina telephone ench'ange system, callfing lines arranged in groups, the lines of eachgroup being arranged in a 'fixedorder,

sections, multiple contact sets 'inzsaid bank, said l nes-terminat ng n sa d contact sets,

a contactbanlrcomprising a plurality of aplurality of line finder switches arranged "10 5 for cooperation with each of said'sections,

the various. groups being so, arrangedin the 7 var ous sections that a different group ap "pears-as a first choice in each of sa1d-seetions, and means operative upon the initiation of a call for puttinginto operation an idle one of the switches which serve a sec;

ftionzof said contact bank in which'the group 7 containing the contactset of the calling line ppears as a first-choice. J s

2. Ina telephone exchange system, call-s ing lines arranged in groups, the lines of each groupbeingi'arranged in a fixed order, a contact bank comprising aplurality of sec tions, multiple contact sets in said bank,

a plurality of line finder switches arranged the various groups being so arranged in the switchesfand means? operative upon the insaid lines terminating-in said, contactsets,

for; cooperation with each 'of said sections, i

itiatio niof a call for putting into operation one of the line finder switches which serves a section of said contact bank in which the group containing the contact set of the calling line appears as a first choice, provided that one of such switches is idle.

1 3. Ina a telephone exchange system, calling lines arranged in groups, the lines of each group being arranged in a fixed order,

trolled the starting of said line finder to prepare for use an idle finder in the group of finders which serves a section of the contact bank in which the group or" lines, to which said allotter is individual, appears as a first choice. i x

=4. In a telephone exchange system, calling lines arranged in groups, the lines of each group being arranged in a fixed order, a contact bank comprising a plurality of sections, multiple contact sets in said bank, said lines terminating in said contact sets, a

plurality of line finder switches arranged for cooperation with each of said sections, the various groups being so arranged in the various'sections that a different group appears as a first choice in each of said sectionsyan allotter switch individual to each of said groups, means to start idle line finders as calls are originated, means to operate an allotter switch each time that a line finder is started to prepare for use an idle finder in the group of finders which serves a section of the contact bank in which the group of lines, to which said allotter is individual, appears as a first choice, provided 'there :be an idle finder in such group, and

means to prepare for use an idle finder in another group of finders in case all of the finders in-the preferred group are'busy.

5.; In a telephone exchange system, calling lines arranged in groups, the lines of each group being arranged in a fixed order, a contact bank comprising a plurality of sec- .-tions, multiple contact sets in said bank, said lines terminating in said contact sets, a plurality of line finder switches arranged for cooperation with each of said sections, the

various groups being'so' arranged in the various sections that'a different group appearslas a first choice in each of said sect1ons,'an allotter switch 'indivldual to each of said groups, means t successively start idle line finders under the control of said allotters as calls are originated, and means to maintain said allotters in positions to control the idle finders which respectively serve sections of the contact bank in which the groups of lines, to whichsaid allotters are individual, appear respectively as first choices.

6. In a telephone exchange system, calling lines arranged in groups, the lines of each group being arranged in a fixed order, a'

contact bank comprising a plurality of sections, multiple contact sets in said bank, said lines'terminating in said contact sets, a plurality of line finuer switches arranged for cooperation with each of said sections, the various groups being so arranged in the various sections that a different group ap- 1 pears as a first choice in each of'said sections an allotter switch individual to each 7 7 group, means to operate an allotter switch to'control. the starting of idle finders in the group of finders which serves the section of the contact bank in which the group of lines, to which said allotter is individual, appears as a first choice, as long as any of these finders are idle, means to prepare for starting line finder switches which serve a subcquent section in case allpreferred line finders are busy, and means operative after a line finder in a subsequent group has been started for causing said allotter to pass over idle line finders in subsequent groups and return to its preferred group and allot a line finder therein, provided that, meanwhile, a

finder in such preferred, group has become idle.

7. In a telephone exchange system, calling as a first choice in each ofsaid sections, a

plurality of multipled brush sets for each of said line finders, there being as many brushes as there are main groups, and means operative upon the initiation of acall for putting into operation an idle one of the switches which serve a section, of said contact bank in which the subgroup, containing ,the contact set of the calling line, appears :as a first choice for the brush set which serves themain line appears. v a

. 8.. In a telephone exchangesystem, calling group in which said-calling lines arrangedin groups, the lines of each groupbeingarranged in a fixedorden a contact bank'cornprising aplurality ofsections, multiple contact sets in said bank a plurality of line finder switches arranged for cooperationwith each of said sections,

the various groups being so arranged in the various sections that a different group appears as a firstchoice in each of said sections, starting'circuitsfor'said line finder to control the starting circuits of all of said line finder switches, and means operative upon the'initiation of a'call for putting into operation an idle one of the switches which serve the section of said contact bank in Whichthe group containing the contactset of the calling line appears as a first choice.

9. In a telephone eXchangefsystem, calling lines arranged in two groups, the lines of each group being arranged in a fixed order, a contact bank comprising two sec-, tions, multiple contact sets in sa d bank,

said lines terminating in said contact sets, a plurality ofline finder switches arranged n my namethis 30th day of December, A.

for cooperation with each of said sections, the group of contact sets which appears as a first choice in the first of said sections I I I s a l 7 said hnes terminating in said contact sets,

and Ineansoperative upon the initiation of a callfor putting into operation an idle one of ,the'switches which serve the section 'in' which the group containing the contact set ot thecalling line appears as a firstichoice." 10. In a telephone exchange system, calling linesarranged in two -groups,the lines of each group being arranged in a fixed order, a contactbank comprising two sections, multiple contact sets in said bank, said lines. terminating in said sections, the group 7 of contact sets which appears as a first choice inthe firstof saidsections being ar-' ranged to appear as-asecond choice in the second ofsaid sections and'vice versa, an

allotter switch individual to each group,

each of said allotter switches being arranged to control thestarting of all of said line finderswitches, and means operative upon a the initiation of a call for puttinginto operationan idle one of the switches which serve thel' section in which the group containing the contact set of the calling line In witness whereof I hereunto subscribe k 1 AMUELB, WILLIAMS, JR. 

